Earlier studies in this laboratory have demonstrated a relation between brain iron and neuroendocrine regulation. The present experiments were designed to learn whether or not intraventricular injection of an iron chelator (deferoxamine mesylate) in the region of the ventromedial hypothalamus and median eminence would affect the estrous cycle. Estrous cyclicity was determined by the vaginal smear technique. Eight of 10 rats injected with iron chelator exhibited a loss of estrous cyclicity of 2 to 4 cycles duration, whereas only 2 of 10 saline injected controls had a period of acyclicity (p less than 0.01, Fisher's exact test). The iron histochemical and histological examination of brain tissue is now in progress.